Purification of Reagents and Solvents

The imidazoUdinonium salt 12 HC1 was shown to be an excellent catalyst for the Diels-Alder reaction of a,P-unsaturated aldehydes 15 (Scheme 2) [3]. Using just 5 mol% of the catalyst at room temperature in a methanol/water mixture (19 1), adducts were obtained in excellent yield (75-99%) and enantiomeric excess (84-93%). The simplicity of these transformations, operating at room temperature in the presence of moisture and air without the need for rigorous purification of solvents and reagents, makes these procedures highly practical and opened up a new area for further research. 

Attention also is directed to other chapters which are useful adjuncts to the present one Inert Gases and Their Purification (Chapter 3), Purification of Solvents and Reagents (Chapter 4), and Joints, Stopcocks, and Valves (Chapter 8). The solvent and chemical resistance of elastomers, which are used in O-ring joints and septa, are discussed in Chapter 8 and Appendix III. 

It is much more convenient to use the collective volumes where the earlier annual volumes of Organic Syntheses are combined in groups of 9 or 10 in the first six collective volumes (Volumes 1-6), and then in groups of 5 for the next four volumes (Volumes 7,8,9, and 10). Useful indices are included at the end of each of the collective volumes that classify methods according to the type of reaction, type of compound prepared, formula of compound prepared, preparation or purification of solvents and reagents, and use of various types of specialized apparatus. 

Antimony trichloride reacts with vitamin D producing an orange colour with a maximum at 500 m/. The reagent also reacts with vitamin A (transient blue colour with a maximum at 620 m/bt), sterols and allied compounds. The colour produced with a vitamin D is not stable, its intensity increasing with time at a rate dependent on the nature and quantity of residual impurities. Purification of solvents and use of different grades of solid have not perceptibly improved this condition. The addition of acetyl chloride and use of ethylene dichloride as solvent have given some improvement. 

Physica.1 Properties. Carbonyl sulfide [463-58-1] (carbon oxysulfide), COS, is a colorless gas that is odorless when pure however, it has been described as having a foul odor. Physical constants and thermodynamic properties are Hsted ia Table 1 (17,18). The vapor pressure has been fitted to an equation, and a detailed study has been made of the phase equiUbria of the carbonyl sulfide—propane system, which is important ia the purification of propane fuel (19,20). Carbonyl sulfide can be adsorbed on molecular sieves (qv) as a means for removal from propane (21). This approach has been compared to the use of various solvents and reagents (22). 

The submitters used reagent-grade solvents and reagents without further purification. The yield of 2-hydroxyimino-2-phenylacetonitrile was 76% when the checkers used technical-grade benzyl cyanide purchased from Wako Pure Chemical Industries, Ltd., Osaka, Japan. The yield was improved to 81% with distilled material, b.p. 75-77° (3 mm.). Benzyl cyanide is also available from Aldrich Chemical Company, Inc. 

All solvents used for general applications were of reagent grade. For special purposes, purification of solvents was effected using standard procedures. All other reagents were used as supplied commercially except as noted. A solution of chloromethyl methyl ether (6 mmole/mL) in methyl acetate was prepared by adding acetyl chloride (141.2 g, 1.96 mol) to a mixture of dimethoxy methane (180 mL, 2.02 mol) and anhydrous methanol (5.0 mL, 0.12 mol).20 The solution was diluted with 300 mL of 1,1,2,2-tetrachloroethane and used as a stock solution for the chloromethylation experiments. 

Much of what needs to be done about the techniques of removing water from glass apparatus and from solvents and reagents has been set out above in a more general context. It remains to point out a few pecularities which characterise the drying process rather than any other purification procedure and to discuss some drying agents. 

Solvents that have been less extensively used are N-methyl-2-pyrrolidinone and hexamethylphosphoric triamide.183 The author of this article183 also discussed the purification of chlorotrimethylsilane, and the anomalous results that may be obtained from the use of impure reagent have been commented on in the case of analyses of pentaerythritol.184 The various methods available for the bulk purification of methyl sulfoxide have been reviewed,185 and a symposium on this compound reviewed its use as a solvent in selected reactions.186... 

A strict vacuum-line technique was used for purifications of solvent, monomer, and initiator, preparation of solutions and polymerization. Polystyryllithium of a degree of polymerization of about 15 was prepared by using n-butyllithium and was used as a seed polymer. Purifications of reagents were most carefully carried out. See the original literature for details 17). 

HPLC is fast and economical in terms of labor and reagents. The effluent fractions come off the column in small volumes of solvents readily available for liquid scintillation counting, and/or further purification steps. 

The procedure described here is a modification of that previously published. Specifically, it is frequently insufficient to use the 2-bromo-2-butene as obtained from the supplier without purification using basic alumina I. Such purification assures facile reaction with lithium. Furthermore, the large volumes of diethyl ether used in the past are unnecessary and may inhibit initiation of the reaction of 2-bromo-2-butene with lithium. Finally, while dry solvents and reagents are required, diethyl ether from a freshly opened can is sufficiently free of water, and distillation from lithium aluminum hydride is unnecessary. 

Hyperforin (containing traces of adhyperforin) was obtained form Dr. W. Schwabe Pharmaceuticals (Karlsruhe, Germany). Methanol and acetonitrile were purchased from Caledon (Georgetown, ON, Canada) in HPLC-grade quality. Purified water from a Milli-Q water purification system (Millipore, Bedford, MA) was used. All other solvents and reagents (Tris buffer, ascorbic acid, formic acid and ammonium formate) were obtained from Sigma-Aldrich (Missisauga, ON, Canada). 

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